Cut the bread into cubes with X slices without cutting all the way through the bottom crust.

Pour the butter-onion garlic mixture carefully into those X cracks using a small spoon and over the top of the bread. Fill those delicious cracks with the grated cheese. (It seems like a lot of work and trouble but it's all worth it. Yes.)Wrap the entire loaf with foil, sealing the sides properly and bake for 15-20 minutes. Remove from the oven and unwrap. Bake for another 10 minutes until the cheese is melted and gooey.